The invention relates to a cosmetic or dermatological composition containing an acidic aqueous medium and at least one crosslinked poly(2-acrylamido-2-methylpropanesulphonic acid) polymer which is neutralized to at least 90%.
The invention also relates to the use of this composition in the cosmetic treatment of keratinous substances, in particular of the skin, hair and mucous membranes, in particular to a non-therapeutic process for depigmentation of the skin.
At different periods in their life, some people witness the appearance on the skin, and more particularly on the hands, of darker or more highly colored blemishes which give the skin a heterogeneous appearance. These blemishes are generally due to significant production of melanin in the epidermis or the dermis of the skin.
These blemishes can be related to a number of phenomena and more especially to aging. In some cases, these blemishes can become cancerous. It is consequently increasingly sought to decrease, indeed remove, these blemishes. Use is made of organic active principles, such as kojic acid, caffeic acid or salicylic acid and its derivatives, in treating these blemishes.
Damaged hair can also be treated with compositions based on acidic active principles, in order to tone it up, to restore its vigor and to strengthen the keratinous fibers.
Compositions conventionally used in the cosmetic or dermatological fields are water-in-oil (W/O) emulsions, oil-in-water (O/W) emulsions or aqueous gels in which it is often difficult, indeed even impossible, to incorporate organic acid active principles, such as kojic acid, caffeic acid or salicylic acid and its derivatives.
These acidic active principles generally have a tendency to recrystallize or to degrade. This results in a more or less significant loss in effectiveness of these compositions, according to the degree of recrystallization or degradation, which goes against the desired objective. In addition, this recrystallization or degradation can modify the overall stability of these compositions as well as their appearance, which can dissuade the user from employing these specific treatment compositions.
The use is known, in dissolving some of these active principles, of W/O or O/W emulsions in which the aqueous phase exhibits an acidic pH. For these emulsions to be stable (non separation of the aqueous and oily phases), it is necessary to use emulsifiers (or surfactants). Unfortunately, these surfactants are often irritating to the skin. In addition, these emulsions often lack freshness on application, which can interfere with their uses during warm periods of the year or in hot countries. An aqueous gel is much more appreciated under these conditions of use. However, its very large amount of water does not allow active principles exhibiting a degree of lipophilic nature to be introduced therein. Moreover, the stability of these gels is mediocre.
The need thus remains for a stable composition having the appearance of a gel, which can be used in particular in the cosmetic or dermatological fields, Which makes possible sufficient solubilization of the acidic a-active principles generally used in these fields for the purpose of maximum effectiveness.
With this objective, the use has already been envisaged, in European Patent Application EP-A-680,748, of acidic compositions in the gel form containing crosslinked cationic copolymers or homopolymers which are substantially soluble in aqueous media, and in particular in water, and which are composed of units resulting from the reaction between (i) a cationic monomer containing ethylenic unsaturation or a cationic mixture of monomers containing ethylenic unsaturation and (ii) a crosslinking agent containing ethylenic polyunsaturation. These gelling agents make it possible to stabilize and to dissolve these acidic active principles in compositions containing aqueous media rich in organic solvent.
The use has also already been envisaged, in European Patent Application EP-A-642,781, as gelling and stabilizing agents, of a crosslinked anionic copolymer which is substantially soluble in water and which is composed of units deriving from the reaction between (i) acrylamide, (ii) 2-acrylamido-2-methylpropanesulphonic acid and (iii) at least one compound containing olefinic polyunsaturation (crosslinking agent) in acidic oil-in-water emulsions containing acidic organic active principles.
These two polymer families exhibit the disadvantage, however, of not allowing the production of spontaneously transparent gels, which is harmful to the aesthetic appearance of the final product. Moreover, in the presence of certain acidic organic active principles, such as glycolic acid, these polymers lose their thickening or gelling power and do not allow formulations of high and stable viscosity to be obtained.
The inventors have discovered, surprisingly, a new family of thickening or gelling polymers allowing acidic cosmetic and dermatological formulations to be obtained in the form of transparent and homogeneous gels making it possible to attain high viscosities which are stable over time at room temperature or at higher temperatures.
Moreover, these polymers make it possible to dissolve and stabilize acidic organicactive principles in a cosmetic or dermatological composition containing an acidic aqueous medium at pH values of less than or equal to 5.
In particular, they make it possible to dissolve and to stabilize organic acid active principles in a cosmetic or dermatological composition containing an acidic aqueous medium rich in organic solvent. Compositions containing an aqueous medium rich in organic solvent is understood to mean a composition containing at least 45% by weight of organic solvent with respect to the total weight of the composition.
Finally, these polymers make it possible to produce gels which are transparent, non-runny, non-stringy, soft and smooth on application.
Thus, a subject of the invention is a cosmetic or dermatological composition containing a cosmetically acceptable acidic aqueous medium and at least one crosslinked poly(2-acrylamido-2-methyl-propanesulphonic acid) polymer neutralized to at least 90%.
The composition of the invention has a certain consistency or behavior; it is not stringy, i.e., it does not form strings when taken with the finger. It is more preferably provided in the form of a gel.
The pH of the aqueous medium is advantageously less than or equal to 5 and in practice preferably in the range from 1 to 4. Above the pH value of 6, the formulation no longer exhibits difficulties.
The crosslinked and virtually or completely neutralized poly(2-acrylamido-2-methylpropanesulphonic acid) polymers in accordance with the invention are water-soluble or swellable in water. They are in general characterized in that they comprise, distributed randomly:
(a) from 90 to 99.9% by weight of units of the following formula (1): 
in which X+ denotes a cation or a mixture of cations, it being possible for at most 10 mol % of the cations X+ to be protons H+; and
(b) from 0.01 to 10% by weight of crosslinking units originating from at least one monomer having at least two olefinic double bonds; the proportions by weight being defined with respect to the total weight of the polymer.
The polymers of the invention preferentially contain a number of units of formula (1) in an amount which is sufficiently high to obtain a hydrodynamic volume of the polymer, in solution in water, having a radius ranging from 10 to 500 nm, with a homogeneous and unimodal distribution.
The more particularly preferred polymers according to the invention comprise from 98 to 99.5% by weight of units of formula (1) and from 0.2 to 2% by weight of crosslinking units.
X+ represents a cation or a mixture of cations selected in particular from a proton, an alkali metal cation, a cation equivalent to that of an alkaline-earth metal or the ammonium ion. More particularly, 90 to 100 mol % of the cations are NH4+ cations and 0 to 10 mol % are protons (H+).
The crosslinking monomers having at least two olefinic double bonds are selected, for example, from dipropylene glycol diallyl ether, polyglycol diallyl ethers, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetrallyloxenthanoyl or other allyl or vinyl ethers polyfunctional alcohols, tetraethylene glycol diacrylate, triallylamine, trimethylolpropane diallyl ether, methylenebisacrylamide or divinylbenzene.
The crosslinking monomers having at least two olefinic double bonds are more particularly selected from those corresponding to the following formula (2): 
in which R1 denotes a hydrogen atom or a C1-C4 alkyl. The crosslinking monomer is preferably methyl (trimethylolpropane triacrylate).
The polymerization reaction of the polymers of the invention produces not only linear chains but also branched or crosslinked molecules of polymer. These molecules can be characterized in particular by their rheological behavior in water but more particularly by dynamic light scattering.
In the case of the characterization of the molecules by dynamic light scattering, the distribution of the hydrodynamic volume of the structures of the polymer is measured. Macromolecules dissolved in water are flexible and surrounded by a solvation envelope formed from water molecules. With charged polymers, such as those of the invention, the size of the molecules depends on the amount of salt in the water. In polar solvents, the uniform charge along the main chain of the polymer results in a significant expansion in the polymerchain. The fact of increasing the amount of salt increases the amount of electrolyte in the solvent and screens the uniform charges of the polymer. In addition to the molecules transported in the solvation envelope, solvent molecules are fixed in the cavities of the polymer. In this case, the solvent molecules form part of the dissolved macromolecules and move at the same average speed. Thus, the hydrodynamic volume describes the linear dimension of the macromolecule and of these solvation molecules.
The hydrodynamic volume vh is determined by the following formula:
vh=M/NAxc3x97(V2+dV1)
with:
M denoting the mass in grams of the undissolved macromolecule;
NA denoting Avogadro""s number;
V1 denoting the specific volume of the solvent;
V2 denoting the specific volume of the macromolecule;
d denoting the mass in grams of the solvent which is associated with 1 gram of undissolved macromolecule.
If the hydrodynamic particle is spherical, it is then easy to calculate the hydrodynamic radius from the hydrodynamic volume by the formula:
Vh=4xcfx80R3/3
with R denoting the hydrodynamic radius.
Cases where hydrodynamic particles are perfect spheres are extremely rare. The majority of synthetic polymers involve compacted structures or ellipsoids of high eccentricity. In this case, the radius is determined with respect to a sphere which is equivalent from a frictional viewpoint to the shape of the particle under consideration.
As a general rule, the determination is carried out with respect to molecular weight distributions and thus with respect to hydrodynamic radius and volume distributions. For polydispersed systems, the distribution of the diffusion coefficients must be calculated. From this distribution, the results relating to the radial distribution and to the distribution of the hydrodynamic volumes is deduced therefrom.
The hydrodynamic volumes of the polymers of the invention are in particular determined by dynamic light scattering from the Stokes-Einstein diffusion coefficients D of formula: D=kT/6xcfx80xcex7R where k is Boltzmann""s constant, T is the absolute temperature in degrees Kelvin, xcex7 is the viscosity of the solvent (water) and R is the hydrodynamic radius.
These diffusion coefficients D are measured according to the method of characterization of a mixture of polymers by laser scattering described in the following references:
(1) Pecora, R; Dynamic Light Scattering; Plenium Press, New York, 1976;
(2) Chu B; Dynamic Light Scattering; Academic Press, New York, 1994;
(3) Schmitz, K S; Introduction to Dynamic Light Scattering; Academic Press, New York, 1990;
(4) Provincher S. W.; Comp. Phys., 27, 213,1982;
(5) Provincher S. W.; Comp. Phys., 27, 229,1982;
(6) ALV Laservertriebgesellschaft mhH, Robert Bosch Str. 47, D-63225 Langen, Germany;
(7) ELS-Reinheimer Strasse 11, D-64846 Gross-Zimmern, Germany; and
(8) Chi Wu et al., Macromolecules, 1995, 28,4914-4919.
The particularly preferred polymers are those exhibiting a viscosity, measured with a Brookfield viscometer in a 2% solution in water at 25xc2x0 C., of greater than or equal to 1000 cPs, preferably ranging from 5000 to 40,000 cPs and more preferably ranging from 6500 to 35,000 cPs.
The at least one crosslinked poly(2-acrylamido-2-methylpropanesulphonic acid) polymer of the invention can be obtained according to the preparation process comprising the following stages:
(a) the 2-acrylamido-2-methylpropanesulphonic acid monomer is dispersed or dissolved in the free form in a tert-butanol or water and tert-butanol solution;
(b) the solution or the dispersion of MPSA monomer obtained in (a) is neutralized with one or a number of inorganic or organic bases, preferably ammonia NH3, in an amount which makes it possible to obtain a degree of neutralization of the sulphonic acid functional groups of the polymer ranging from 90 to 100%;
(c) the crosslinking monomer or monomers is/are added to the solution or dispersion obtained in (b); and
(d) a conventional radical polymerization is carried out in the presence of free radical initiators at a temperature ranging from 10 to 150xc2x0 C., the polymer precipitating in the solution or dispersion based on tert-butanol.
The at least one virtually or completely neutralized crosslinked poly(2-acrylamido-2-methylpropanesulphonic acid) polymer is present in the cosmetic or dermatological compositions of the invention in concentrations preferably ranging from 0.01 to 20% by weight with respect to the total weight of the composition and more preferably from 0.1 to 10% by weight.
The compositions according to the invention can contain cosmetic or dermatological acidic organic active principles dissolved and stabilized in the acidic aqueous medium, in the presence of at least one crosslinked poly(2-acrylamido-2-methylpropanesulphonic acid) polymer as defined above.
Mention may be made, as organic acid active principles which can be dissolved in the composition of the invention, of ascorbic acid, kojic acid, citric acid, caffeic acid, salicylic acid and its derivatives (for example, 5-n-octanoyl- or 5-decanoylsalicylic acid), xcex1-hydroxy acids, such as lactic acid, methyllactic acid, glucuronic acid, glycolic acid, pyruvic acid, 2-hydroxybutanoic acid, 2-hydroxypentanoic acid, 2-hydroxyhexanoic acid, 2-hydroxyheptanoic acid, 2-hydroxyoctanoic acid, 2-hydroxynonanoic acid, 2-hydroxydecanoic acid, 2-hydroxyundecanoic acid, 2-hydroxydodecanoic acid, 2-hydroxytetradecanoic acid, 2-hydroxyhexadecanoic acid, 2-hydroxyoctadecanoic acid, 2-hydroxytetracosanoic acid or 2-hydroxyeicosanoic acid, mandelic acid, benzoic acid, phenyllactic acid, gluconic acid, galacturonic acid, citric acid, aleuritic acid, ribonic acid, tartronic acid, tartaric acid, malic acid, fumaric acid, retinoic acid and its derivatives, benzene-1,4-di(3-methylidene-10-camphorsulphonic acid), urocanic acid, 2-phenylbenzimidazole-5-sulphonic acid, xcex1-(2-oxo-3-bornylidene)toluene4-sulphonic acid or 2-hydroxy4-methoxy-5-sulphonic acid. It is also possible to use any natural or synthetic compound containing such acids, such as plant extracts and more especially fruit extracts. It is also possible to dissolve acidic xanthine derivatives (caffeine, theophylline), xcex2-glycyrrhetinic acid or asiatic acid.
The compositions of the invention contain a cosmetically acceptable aqueous medium, i.e., a medium compatible with all keratinous substances, such as the skin, nails, mucous membranes and hair, or any other cutaneous region of the body.
The cosmetically or dermatologically acceptable medium of the compositions according to the invention is more particularly composed of water and optionally of cosmetically or dermatologically acceptable organic solvents.
The organic solvents can represent from 5% to 98% of the total weight of the composition. They can be selected from hydrophilic organic solvents, lipophilic organic solvents, amphiphilic solvents and their mixtures.
Mention may be made, among hydrophilic organic solvents, for example, of linear or branched lower monoalcohols having from 1 to 8 carbon atoms, such as ethanol, propanol, butanol, isopropanol or isobutanol; polyethylene glycols having from 6 to 80 ethylene oxide units; polyols, such as propylene glycol, isoprene glycol, butylene glycol, glycerol or sorbitol; mono- or dialkyl isosorbides in which the alkyl groups have from 1 to 5 carbon atoms, such as dimethyl isosorbide; or glycol ethers, such as diethylene glycol monomethyl or monoethyl ether and propylene glycol ethers, such as dipropylene glycol methyl ether.
Mention may be made, as amphiphilic organic solvents, of polyols, such as polypropylene glycol (PPG) derivatives, for example esters of polypropylene glycol and of fatty acid or ethers of PPG and of fatty alcohol, such as PPG-23 oleyl ether and PPG-36 oleate.
Mention may be made, as lipophilic organic solvents, for example, of fatty esters, such as diisopropyl adipate or dioctyl adipate, or alkyl benzoates.
In order for the cosmetic or dermatological compositions of the invention to be more pleasant to use, i.e., softer on application, more nourishing, and more emollient, it is possible to add a fatty phase to the medium of these compositions.
The fatty phase preferably represents from 0% to 50% of the total weight of the composition. This fatty phase can contain one or a number of oils preferably selected from:
water-soluble or liposoluble, organomodified or non-organomodified, linear, branched or cyclic, volatile or non-volatile silicones;
mineral oils, such as liquid paraffin or liquid petrolatum;
oils of animal origin, such as perhydrosqualene;
oils of plant origin, such as sweet almond oil, avocado oil, castor oil, olive oil, jojoba oil, sesame oil, groundnut oil, macadamia oil, grape seed oil, rapeseed oil or coconut oil;
synthetic oils, such as purcellin oil or isoparaffins;
fluorinated and perfluorinated oils; and
esters of fatty acids, such as purcellin oil.
The fatty phase can also contain, as fatty substance, one or a number of fatty alcohols, fatty acids such as stearic acid or waxes such as paraffin wax, polyethylene waxes, carnauba wax and beeswax.
The compositions of the invention can contain adjuvants usual in the cosmetic and dermatological fields: other conventional hydrophilic or lipophilic gelling or thickening agents; hydrophilic or lipophilic active principles; preservatives; antioxidants; fragrances; emulsifiers; moisturizing agents; pigmenting agents; depigmenting agents; keratolytic agents; vitamins, emollients; sequestering agents; surfactants; polymers; basifying or acidifying agents; fillers; agents for combatting free radicals; ceramides; sunscreen agents, in particular ultraviolet screening agents; insect repellents; slimming agents; coloring materials; bactericides; or antidandruff agents. The amounts of these different adjuvants are those conventionally used in the fields under consideration.
Of course, the person skilled in the art will take care to choose the possible compound or compounds to be added to the composition according to the invention so that the advantageous properties intrinsically attached to the composition in accordance with the invention are not, or not substantially, detrimentally affected by the envisaged addition.
The compositions according to the invention can be provided in all the forms appropriate for a topical application, in particular in the form of solutions of the lotion or serum type, in the form of aqueous gels or in the form of emulsions obtained by dispersion of a fatty phase in an aqueous phase (O/W) or vice versa (W/O), with a liquid or semi-liquid consistency, such as milks, more or less smooth creams or pastes. These compositions are prepared according to the usual methods.
The compositions according to the invention can be used as rinse-out hair products or as leave-in hair products, in particular for washing, caring for, conditioning or form retention of the hairstyle or shaping keratinous fibers, such as the hair.
The inventive compositions can be styling products, such as hair setting lotions, blow-drying lotions or fixing and styling compositions. The lotions can be packaged in various forms, in particular in vaporizers or pump-action sprays or in aerosol containers, in order to provide for application of the composition in the vaporized form or in the foam form. Such packaging forms are indicated, for example, when it is desired to obtain a spray or a foam for fixing or treating the hair.
The compositions of the invention can also be shampoos or compositions of a rinse-out or leave-in nature to be applied before or after shampooing, dyeing, bleaching, perming or hair straightening.
The compositions of the invention can also be used as a care or hygiene product, such as protection, treatment or care creams for the face, for the hands or for the body, protection or care body milks or lotions, gels or foams for caring for the skin and mucous membranes or for cleansing the skin.
The compositions of the invention can also be used as anti-sun products.
The compositions can also consist of solid preparations constituting cleansing bars or soaps.
The compositions of the invention can also be used as oral care products, such as toothpastes.
The compositions can be make-up products.
Another subject of the invention is a process for the non-therapeutic cosmetic treatment of the skin, scalp, hair, eyelashes, eyebrows, nails or mucous membranes, characterized in that a composition as defined above is applied on the skin, scalp, hair, eyelashes, eyebrows, nails or mucous membranes according to the usual technique for the use of this composition. For example: application of creams, gels, serums, lotions or milks on the skin, scalp or mucous membranes. The type of treatment depends on the acidic active principle or principles dissolved in the composition.
More especially, the invention relates to a non-therapeutic process for depigmenting the skin of the human face or body which consists in applying a composition as defined above on the skin.
A further subject of the invention is the use of the above composition in preparing a pomade or an ointment intended for the therapeutic treatment of the human face or body, including the hands, in particular for treating acne and blackheads on greasy skins.
A further subject of the invention is the use of a polymer as defined above for gelling or thickening a cosmetic or dermatological composition containing an acidic aqueous medium.
A further subject of the invention is the use of a polymer as defined above for gelling or thickening a cosmetic or dermatological composition containing an aqueous medium rich in organic solvent.
A further subject of the invention is the use of a polymer as defined above for dissolving and stabilizing an organic acid active principle in a cosmetic or dermatological composition containing an acidic aqueous medium.
A further subject of the invention is the use of a polymer as defined above for dissolving and stabilizing an organic acid active principle in a cosmetic or dermatological composition containing an aqueous medium rich in organic solvent.